Sean Schemmel, the voice of Adult Goku, confirmed at ComiCon 2012 (London) that he passed out while recording a Super Saiyan 4 transformation.
Contrary to popular belief, there IS a manga of Dragon Ball GT. However, it came AFTER the anime and was not created by Akira Toriyama, therefore making it unofficial to the official Toriyama-verse.
GT was the brainchild of Toei Animation and was not based on a manga by Akira Toriyama . However, Toriyama did make some contributions to the series, namely sketches of the main characters, their spaceships, etc.
Many people believe that Dragon ball GT is not created by toriyama and that it's not "canon" to his manga, according to a interview it's stated that toriyama did oversee the production of Dragon ball GT meaning he was involved, he also created a sketch of the logo of the continuation, created the main character designs such as vegeta having a haircut and a mustache and also was involved on creating the early plot of the continuation.
Since the release of the new Dragon Ball Z movies "Battle of Gods" (2013), "Resurrection F" (2015) and the new T.V. series "Dragon Ball Super" (2015), Dragon Ball GT is no longer canon to the original series, however Dragon Ball creator Ajira Toriyama said, he saw Dragon Ball GT as a good Alternate Ending to the original series.